Expression of SA5K, a secretion antigen of Mycobacterium tuberculosis, inside human macrophages and in sputum from tuberculosis patients

Correlation between Sputum Bacterial Culture Positive Rate and Drug Sensitivity Test Results and Disease Severity inInpatients and Its Clinical Significance: A SystematicReview and Meta-Analysis

Objective. To systematically evaluate the correlation between the positive rate of sputum bacterial culture and the results of drug sensitivity test and the severity of the disease and its clinical significance, so as to provide evidence-based medicine for clinical application. Methods. PubMed, Embase, ScienceDirect, Cochrane Library, China Knowledge Network Database (CNKI), China VIP Database, Wanfang Database, and China Biomedical Literature Database (CBM) online database were used. The retrieval time limit was from the establishment of the database to the present. Data for all included studies were extracted by two independent researchers, and the risk of bias for the quality of each included study was assessed by the Cochrane Handbook 5.1.0 criteria. RevMan5.4 statistical software was used to analyze the collected data by meta. Results. In the end, 6 RCT articles were included. Overall, 613 samples were included in 6 RCT studies. The correlation between the positive rate of sputum bacterial culture in inpatients and the severity of the disease was meta-analyzed. The heterogeneity test results showed that Chi2 = 177.20, df = 3, P < 0.00001, and I2 = 98%, indicating that there was obvious heterogeneity among the included research data. It was considered that there was a correlation between the positive rate of sputum bacterial culture and the severity of the disease. The correlation between the results of the drug sensitivity test of inpatients and the severity of the disease was evaluated. The results of the heterogeneity test showed that Chi2 = 0.00, df = 1, P = 1 > 0.05, and I2 = 0%, indicating that there was no heterogeneity among the included research data. In addition, the combined effect of WMD was analyzed by the fixed effect model. The combined effect dose WMD test was Z = 6.58 (P < 0.00001). It was considered that there was a correlation between the results of the drug sensitivity test and the severity of the disease. Conclusion. There is a correlation between positive sputum culture and drug sensitivity test results and the severity of the disease in hospitalized patients. In clinical practice, for hospitalized patients, the positive sputum bacterial culture rate and drug sensitivity test results can be used to guide the appropriate use of antibiotics. Due to the low input from the literature, more studies with higher methodological quality and longer follow-up are needed for further validation.

Mycobacterium tuberculosis low molecular weight T-cell antigen Mtb8.4 has heme-binding and fiber-forming properties

Mtb8.4, a secretory T-cell antigen of Mycobacterium tuberculosis, is important for providing an antigen-specific immune response. In this study, we showed Mtb8.4 to have both heme-binding and fibril-forming properties, using experimental and in silico methods. High absorbance at 410 nm and interaction with hemin-agarose demonstrated its heme-binding nature. Titration of Mtb8.4 with heme resulted in 1:1 stoichiometry. The heme-binding pocket in Mtb8.4 was identified by molecular modeling, and binding residues were predicted using molecular docking. The molecular dynamics simulations of apo- and heme-bound Mtb8.4 confirmed that the heme group forms a stable complex. Transmission electron microscopy analyses and dye-binding assays showed that Mtb8.4 forms fibers. Computational studies predicted that the C-terminal sequence (⁹³ AAQYIGLVESV¹⁰³ ) is important for forming fibers. In silico analyses further anticipated the probable epitope (⁸² AMAAQLQAV⁹⁰ ) of Mtb8.4. The fiber-forming properties of Mtb8.4 could be advantageous from a vaccine perspective for aggregate/fibril-based vaccine delivery or it might influence the epitope presentation of Mtb8.4.

Whole genome identification of Mycobacterium tuberculosis vaccine candidates by comprehensive data mining and bioinformatic analyses

Background

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), infects ~8 million annually culminating in ~2 million deaths. Moreover, about one third of the population is latently infected, 10% of which develop disease during lifetime. Current approved prophylactic TB vaccines (BCG and derivatives thereof) are of variable efficiency in adult protection against pulmonary TB (0%–80%), and directed essentially against early phase infection.

Methods

A genome-scale dataset was constructed by analyzing published data of: (1) global gene expression studies under conditions which simulate intra-macrophage stress, dormancy, persistence and/or reactivation; (2) cellular and humoral immunity, and vaccine potential. This information was compiled along with revised annotation/bioinformatic characterization of selected gene products and in silico mapping of T-cell epitopes. Protocols for scoring, ranking and prioritization of the antigens were developed and applied.

Results

Cross-matching of literature and in silico-derived data, in conjunction with the prioritization scheme and biological rationale, allowed for selection of 189 putative vaccine candidates from the entire genome. Within the 189 set, the relative distribution of antigens in 3 functional categories differs significantly from their distribution in the whole genome, with reduction in the Conserved hypothetical category (due to improved annotation) and enrichment in Lipid and in Virulence categories. Other prominent representatives in the 189 set are the PE/PPE proteins; iron sequestration, nitroreductases and proteases, all within the Intermediary metabolism and respiration category; ESX secretion systems, resuscitation promoting factors and lipoproteins, all within the Cell wall category. Application of a ranking scheme based on qualitative and quantitative scores, resulted in a list of 45 best-scoring antigens, of which: 74% belong to the dormancy/reactivation/resuscitation classes; 30% belong to the Cell wall category; 13% are classical vaccine candidates; 9% are categorized Conserved hypotheticals, all potentially very potent T-cell antigens.

Conclusion

The comprehensive literature and in silico-based analyses allowed for the selection of a repertoire of 189 vaccine candidates, out of the whole-genome 3989 ORF products. This repertoire, which was ranked to generate a list of 45 top-hits antigens, is a platform for selection of genes covering all stages of M. tuberculosis infection, to be incorporated in rBCG or subunit-based vaccines.

The secretion antigen SA5K has a role in the adaptation of Mycobacterium bovis bacillus Calmette-Guérin to intracellular stress and hypoxia

The Mycobacterium tuberculosis TB8.4 (Rv1174c) gene encodes a secreted protein of 8.4 kDa (TB8.4) which has been suggested to be involved in reactivation of dormant mycobacteria. We have previously reported that inactivation of an identical gene (sa5k) in Mycobacterium bovis BCG causes impaired ability of the mutant strain (BCGsa5k::aph) to grow inside human macrophages. This study aimed to investigate the role of TB8.4 in the reactivation of aged cultures of BCG as well as the role of the sa5k gene in the resistance of BCG to intracellular stress conditions and adaptation to hypoxia. Although when added to aged cultures of BCG, TB8.4 caused a statistically significant increase in the number of colony-forming units, a similar effect was obtained in cultures incubated with BSA, suggesting a non-specific growth stimulation by TB8.4. Compared to parental BCG, the BCGsa5k::aph strain showed an increased susceptibility to reactive oxygen and nitrogen intermediates and to acid stress and an impaired ability to adapt to reduced O2 concentrations, when tested in the oxygen-limited Wayne culture system. These results suggest that the product of the sa5k gene (SA5K protein) has a role in both resistance of BCG to intracellular stress and in its adaptation to hypoxia.

Disruption of the gene encoding for secretion antigen SA5K affects growth of Mycobacterium bovis bacillus Calmette-Guerin in human macrophages and in mice

An 8.3-kDa secretory antigen of Mycobacterium bovis bacillus Calmette-Guerin (BCG), called SA5K, was previously identified and characterized in our laboratory. Sequence analysis of the BCG sa5k gene, including the corresponding promoter region, showed that it is identical to the homologous gene in Mycobacterium tuberculosis (Rv1174c). No significant homology with other proteins was found and the physiologic role of SA5K for mycobacteria remains unknown. In the present study, a BCG mutant strain (BCGsa5k::aph) was constructed by allelic exchange involving the replacement of the sa5k gene with a kanamycin-inactivated copy. Mutant and parental strains showed similar growth rates in liquid medium, suggesting that the loss of the sa5k gene does not affect the in vitro growth of BCG. Nevertheless, BCGsa5k::aph showed a reduced ability to grow in human macrophages compared with the wild-type BCG, suggesting that SA5K is involved in intracellular survival/multiplication mechanisms. The mutant strain was also attenuated in vivo in a mouse infection model, showing impaired growth/survival in spleen and liver and fewer and smaller granulomatous lesions compared to the parental strain. Complementation of the mutation restored the parental phenotype. Taken together, results presented in this study suggest a role for SA5K in the growth capacity of BCG both in an intracellular milieu and in infected mice.